FMCW反射计检测距离影响因素分析

Analysis of the Influence Factors of FMCW Reflectometry on Measurement Distance

频率调制连续波(FMCW)反射计以其高动态范围和窄的空间分辨率优势,在光网络检测、集成光路诊断和光纤传感等领域有着广泛的应用前景。在介绍FMCW反射计基本原理的基础上,分析了光源扫描重复频率、光源功率与FMCW反射计检测距离之间的关系,并探讨了光源相干长度和相位噪声对检测距离的影响。理论分析表明,当待测光纤的长度接近光源的相干长度时,中频信号和相位噪声之间的信噪比会急剧下降,所以FMCW反射计要使用高相干性的光源和一定的相位噪声补偿方法才能应用于长距离的光纤检测。

Owing to its high dynamic range, narrow spatial resolution FMCW reflectometry can be widely used in the fields of optical network test, optical IC diagnosis, and fiber optic sensor. On the basis of introducing the basic principle of FMCW reflectometry, the relationship among the repetition frequency of the light source scanning, light source power and the detection distance of the FMCW reflectometry is analyzed. The influence of coherence length and phase noise of the light source on the detection distance is discussed, the theoretical analysis shows that when the length of the tested fiber is close to the coherent length of the light source, the SNR between IF signal and phase noise would be reduced sharply. Therefore, only using light source with high coherence and certain phase noise compensation method, can the FMCW reflectometry be used in the long-distance test of optical fibers.